Figuring out Kaley Cuoco’s bubbly character Penny may have been more difficult than quantum physics for the guys behind The Big Bang Theory.

Co-creator Chuck Lorre and former Warner Bros. Television Group chairman Peter Roth took time out this week to look back on the original, unaired pilot of the hit sitcom while appearing on the debut episode of Jessica Radloff’s The Official Big Bang Theory podcast.

Reflecting on how Cuoco reshaped Penny, the two admitted that the beloved character, an aspiring actress who moves into the apartment across the hall from Sheldon (Jim Parsons) and Leonard (Johnny Galecki), was initially “one-dimensional” and a cliché.

“We had so many episodes to go before we started to understand that there was a brilliance to Penny’s character that we had not explored,” Lorre said. “We did the very clichéd — in the beginning — goofy blonde who says foolish things. It was a clichéd character, the dumb blonde. We missed it. We didn’t have that right away — that what she brought to this story, to these other characters, was an intelligence that they didn’t have. A kind of intelligence that was alien to them. You know, intelligence about people and relationships and family.”